In the field of medicine, imaging and image guidance are a significant component of clinical care. From diagnosis and monitoring of disease, to planning of the surgical approach, to guidance during procedures and follow-up after the procedure is complete, imaging and image guidance provides effective and multifaceted treatment approaches, for a variety of procedures, including surgery and radiation therapy. Targeted stem cell delivery, adaptive chemotherapy regimens, and radiation therapy are only a few examples of procedures utilizing imaging guidance in the medical field. Optical tracking systems, used during a medical procedure, track the position of a part of the instrument that is within line-of-site of the optical tracking camera. These optical tracking systems also require a reference to the patient to know where the instrument is relative to the target (e.g., a tumour) of the medical procedure, or to accurately assess positioning of relative parts of patient anatomy or orthopedic medical devices.
In some surgeries, a patient reference device that includes an optically-trackable component that the navigation system is capable of tracking is fixedly attached to the patient. Provided a proper registration process in undertaken, the navigation system is then able to determine the position of patient anatomy in its coordinate space, so that it is able to track (and display) patient anatomy relative to tracked instruments and devices by also tracking the patient reference device.
In some cases, the patient reference device may be inadvertently bumped during the surgery which can move the patient reference device, cause it to break, or cause the bone to which it is attached to fracture. If the device moves relative to the patient, then the registration is lost and the surgery must either proceed without navigation or it must be stopped to reattach the device and re-perform the registration process. At worst the movement of the patient reference device is not noticed and the surgery proceeds using an inaccurate registration. Accordingly, it would be advantageous to reduce the likelihood of loss of registration and to accurately determine whether re-registration is necessary.